docs: def show(cmap, var, vmin=None, vmax=None):
      '''Show a colormap for a chosen input variable var side by side with
      black and white and jet colormaps.
  
      :param cmap: Colormap instance
      :param var: Variable to plot.
      :param vmin=None: Min plot value.
      :param vmax=None: Max plot value.
  
      '''
  
      # get variable data
      lat, lon, z, data = read(var)
  
      fig = plt.figure(figsize=(16, 12))
  
      # Plot with grayscale
      ax = fig.add_subplot(3, 1, 1)
      map1 = ax.scatter(lon, -z, c=data, cmap='gray', s=10, linewidths=0., vmin=vmin, vmax=vmax)
      plt.colorbar(map1, ax=ax)
  
      # Plot with jet
      ax = fig.add_subplot(3, 1, 2)
      map1 = ax.scatter(lon, -z, c=data, cmap='jet', s=10, linewidths=0., vmin=vmin, vmax=vmax)
      plt.colorbar(map1, ax=ax)
  
      # Plot with cmap
      ax = fig.add_subplot(3, 1, 3)
      map1 = ax.scatter(lon, -z, c=data, cmap=cmap, s=10, linewidths=0., vmin=vmin, vmax=vmax)
      ax.set_xlabel('Longitude [degrees]')
      ax.set_ylabel('Depth [m]')
      plt.colorbar(map1, ax=ax)
  
      plt.suptitle(var)